Question

Cau 1 :

Cho 1/c = 1/2(1/a+1/b) (với a,b,c khác 0 ; b khác c ) chứng minh rằng a/b=a-c/c-b

 

Answer 1

1/c =1/2.(1/a + 1/b)

=> 1/c . 2 = a/ab + b/ab

=> 2/c = a+b/ab

=> 2ab = (a+b).c

=>ab + ab = ac + bc

=> ab -bc = ac- ab

=> b(a-c) = a(c-b)

=> a/b = a-c/c-b

Answer 2

1/c=1/2(1/a+1/b)

=> 1/c.2=a/ab+b/ab

=>2/c=a+b/ab

=>2ab=(a+b).c

=>ab+ab=ac+bc

=>ab-bc=ac-ab

=>b.(a-c)=a.(c-d)

=>a/b=a-c/cb

Answer 3

Ta có 2/a=1/b+1/c

<=> 2/a= b/bc+a/bc

<=> 2bc= ab+ac

<=>bc+bc=ab+ac

<=> ab-bc=bc-ac

<=> b(a-c)=c(b-a)

<=>b/c=(b-a)/(a-c)